Field of the Invention
The present invention relates to a technique for determining a type of a recording material with high accuracy and controlling an image forming condition according to a determination result.
Description of the Related Art
Conventionally, in some cases, image forming apparatuses, such as copying machines and printers, include sensors for determining types of recording materials within the image forming apparatuses. These apparatuses can automatically determine the types of the recording materials and control transfer conditions (i.e., transfer voltages and conveyance speeds of the recording materials at the time of transfer) and fixing conditions (i.e., fixing temperatures and the conveyance speeds of the recording materials at the time of fixing) according to the determined results.
Japanese Patent Application Laid-Open No. 2010-283670 describes an image forming apparatus provided with a recording material determination unit which illuminates a recording material with light and captures the light reflected on the recording material as an image by a complementary metal oxide semiconductor (CMOS) sensor to determine a type of the recording material. The image forming apparatus controls a transfer voltage, a fixing temperature, and a conveyance speed, of the recording material according to the type of the recording material determined by the recording material determination unit. Based on such a process, a high quality image can be formed on the recording material.
Generally, there are two setting methods when recording materials are set in a cassette and the like of an image forming apparatus. One method is for setting the recording materials so as to be conveyed to a direction parallel to a long side direction of the recording material and the other method is for setting the recording materials so as to be conveyed to a direction parallel to a short side direction of the recording material. The former is referred to as a longitudinal conveyance state and the latter is referred to as a lateral conveyance state.
In addition, it is known that a recording material has a predetermined fiber direction (also referred to as a grain direction) depending on its type. When a same recording material is captured by a CMOS sensor in the longitudinal conveyance state and the lateral conveyance state, different images are respectively captured according to a difference in a fiber direction of the recording material. Accordingly, despite the same type of the recording material, it may be erroneously determined as a different type of the recording material. When such errors occur, an image may be formed using an image forming condition not suitable for the recording material, and an image quality may be lowered in some cases.
Japanese Patent Application Laid-Open No. 2010-283670 describes a configuration which includes two light sources for illuminating a recording material with light from different directions for suppressing influence of a fiber direction of the recording material. The two light sources are configured so that the directions of the light emitted therefrom are orthogonal to each other. Further, according to Japanese Patent Application Laid-Open No. 2010-283670, two images obtained by the two light sources are used to determine a type of the recording material and to determine an image forming condition.
The configuration described in Japanese Patent Application Laid-Open No. 2010-283670 can reduce the influence on determination accuracy of the fiber direction of the recording material. However, the necessity to provide two light sources causes increase in the cost of the image forming apparatus.